Who are the Rightly Guided Caliphs (al-Khulafa al-Rashidun al-Mahdiyyun) after the Messenger of Allah, peace be upon him?

The Rightly Guided Caliphs are four: Abu Bakr, Umar, Uthman, and Ali —may Allah be pleased with them. The duration of their caliphate was thirty years. And there are twelve just rulers who govern the people according to Allah's law; the first of them are the four Rightly Guided Caliphs, then after them come those whom Allah wills, among whom is the Mahdi.